The present invention relates in the technical field of an image reading apparatus which is used to digital photoprinters and the like to photoelectrically read an image recorded on a film and output the image as recording image data by subjecting the image to specific image processing.
Images recorded on photographic films (hereinafter, referred to as films) such as a negative film, a reversal film and the like are conventionally printed onto light-sensitive materials (photographic papers) by so-called direct exposure, that is, a method in which an image carried by a film is projected onto the light-sensitive material for exposure.
In contrast, recently, printers making use of digital exposure, have become commercially practical that is, digital photoprinters which photoelectrically read an image recorded on a film, convert the thus read image into a digital signal and thereafter apply various steps of image processing to the digital signal to thereby provide recording image data, record the image (latent image) on a light-sensitive material by scan exposing it with recording light which is modulated in accordance with the image data, and produce a print.
In digital photoprinters, exposure conditions are determined by photoelectrically reading the film and carrying out gradation correction and the like by image (signal) processing. As a result, the digital photoprinters can freely perform an editing job for print images such as composition of a plurality of images to a composite image, division of a single image into segments by processing the images and various types of image processing such as color/density adjustments, edge enhancement and the like and output prints which are freely processed in accordance with a specific use. Further, the image data of a printed image can be supplied to computers and the like and saved in recording mediums such as a floppy disc and the like.
In addition, the digital photoprinters can output a print which has better image quality and has better resolution, color/density reproducibility and the like as compared with a print produced by conventionally direct exposure.
The digital photoprinters essentially comprise an image reading apparatus (input apparatus) which is composed of a scanner for photoelectrically reading an image recorded on a film and converting it into image data and an image processing device for processing the image data (subjecting it to image processing) to thereby determine exposure conditions, namely, making the image data to recording image data and a printer (output device) for scan exposing a photosensitive material in accordance with the recording image data, subjecting it to development processing and outputting the image data as a print.
In the scanner, the reading light emitted from a light source is applied to the film so as to obtain projecting light which carries the image recorded on the film, the projecting light is projected onto an image sensor such as a CCD sensor or the like at a sufficiently focused position by an imaging lens to read the image photoelectrically. The image is then subjected to various types of image processing, when necessary, and thereafter supplied to the image processing device as the image data (image data signal) of the film. In the scanner, the film is fed frame by frame by a carrier mounted thereon so that the images recorded to the respective frames of the film are successively read one by one.
The image processing device sets the image processing conditions from the thus obtained image data, subjects the image data to image processing in accordance with the set image processing conditions and supplies the image data to the printer as processed recording image data (exposure conditions).
In the printer, in the case of an apparatus making use of light beam scanning exposure, for example, light beams are modulated in accordance with the image data supplied from the image processing device and deflected in a main scanning direction. Also, a photosensitive material is conveyed in an auxiliary scanning direction which is normal the main scanning direction. In this manner, the photosensitive material is exposed to (or printed by) the light beams carrying an image to thereby form a latent image. The photosensitive material is then subjected to development processing and the like in accordance with the nature of the photosensitive material. A print (photograph) reproducing the image recorded on the film is thereby obtained.
When the image is read by the photoprinters as described above, the image processing conditions are ordinarily determined from the prescanned image data which is obtained by roughly reading the image recorded on the film and finely scanned image data is processed in accordance with the image processing conditions and output to the printer as the recording image data.
Further, conventional photoprinters employing direct exposure also read an image recorded on a film by an image sensor before the image is printed on a photosensitive material and determine exposure conditions such as an amount of insertion of a color filter in exposure, the stop value of the quantity of light, and the like from the image data of the image.
However, in the above reading of the image, since the characteristic value (base density) of a negative film is reflected to the image data, there may be a situation where proper image processing conditions (namely, exposure conditions) corresponding to the image recorded on a film cannot be determined and a resulting print is improperly made.
To deal with this problem, the direct-exposure type photoprinters effect printing after they read the images of a plurality of frames, for example, the images of all the frames by the image sensor, calculate the characteristic value of the negative film from the image data of all the frames and determine the exposure conditions for each frame using the characteristic value of the negative film and the image information of each frame.
The characteristic value of the negative film is generally determined using the average density value of an image which is liable to be affected by so-called color failure. Thus, the method using the average density value cannot determine the characteristic value of the negative film with pinpoint accuracy and cannot determine preferable image processing conditions in many cases.
In addition, the effect applied to the characteristic value of the negative film by the exceptional value of a frame with failure is reduced by means of the image data of a plurality of frames. However, since ordinary photographs have a plurality of successive frames where similar images (scenes) are recorded, when these frames have failure, the characteristic value of the negative film cannot be also determined with pinpoint accuracy.